/*
 * Copyright 2021 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "modules/skottie/src/effects/Effects.h"

#include "include/core/SkCanvas.h"
#include "include/core/SkM44.h"
#include "include/core/SkPicture.h"
#include "include/core/SkPictureRecorder.h"
#include "include/core/SkTileMode.h"
#include "include/effects/SkRuntimeEffect.h"
#include "modules/skottie/src/Adapter.h"
#include "modules/skottie/src/SkottieJson.h"
#include "modules/skottie/src/SkottieValue.h"
#include "modules/sksg/include/SkSGRenderNode.h"

#include <array>

namespace skottie::internal {
namespace {
// This shader maps its child shader onto a sphere.  To simplify things, we set it up such that:
//
//   - the sphere is centered at origin and has r == 1
//   - the eye is positioned at (0,0,eye_z), where eye_z is chosen to visually match AE
//   - the POI for a given pixel is on the z = 0 plane (x,y,0)
//   - we're only rendering inside the projected circle, which guarantees a quadratic solution
//
// Effect stages:
//
//   1) ray-cast to find the sphere intersection (selectable front/back solution);
//      given the sphere geometry, this is also the normal
//   2) rotate the normal
//   3) UV-map the sphere
//   4) scale uv to source size and sample
//   5) apply lighting model
//
// Note: the current implementation uses two passes for two-side ("full") rendering, on the
//       assumption that in practice most textures are opaque and two-side mode is infrequent;
//       if this proves to be problematic, we could expand the implementation to blend both sides
//       in one pass.
//
static constexpr char gSphereSkSL[] = "uniform shader child;"

    "uniform half3x3 rot_matrix;"
    "uniform half2 child_scale;"
    "uniform half side_select;"

    // apply_light()
    "%s"

    "half3 to_sphere(half3 EYE) {"
    "half eye_z2 = EYE.z*EYE.z;"

    "half a = dot(EYE, EYE),"
    "b = -2*eye_z2,"
    "c = eye_z2 - 1,"
    "t = (-b + side_select*sqrt(b*b - 4*a*c))/(2*a);"

    "return half3(0, 0, -EYE.z) + EYE*t;"
    "}"

    "half4 main(float2 xy) {"
    "half3 EYE = half3(xy, -5.5),"
    "N = to_sphere(EYE),"
    "RN = rot_matrix*N;"

    "half kRPI = 1/3.1415927;"

    "half2 UV = half2("
    "0.5 + kRPI * 0.5 * atan(RN.x, RN.z),"
    "0.5 + kRPI * asin(RN.y)"
    ");"

    "return apply_light(EYE, N, child.eval(UV*child_scale));"
    "}";

// CC Sphere uses a Phong-like lighting model:
//
//   - "ambient" controls the intensity of the texture color
//   - "diffuse" controls a multiplicative mix of texture and light color
//   - "specular" controls a light color specular component
//   - "roughness" is the specular exponent reciprocal
//   - "light intensity" modulates the diffuse and specular components (but not ambient)
//   - "light height" and "light direction" specify the light source position in spherical coords
//
// Implementation-wise, light intensity/height/direction are all combined into l_vec.
// For efficiency, we fall back to a stripped-down shader (ambient-only) when the diffuse & specular
// components are not used.
//
// TODO: "metal" and "reflective" parameters are ignored.
static constexpr char gBasicLightSkSL[] = "uniform half l_coeff_ambient;"

    "half4 apply_light(half3 EYE, half3 N, half4 c) {"
    "c.rgb *= l_coeff_ambient;"
    "return c;"
    "}";

static constexpr char gFancyLightSkSL[] = "uniform half3 l_vec;"
    "uniform half3 l_color;"
    "uniform half l_coeff_ambient;"
    "uniform half l_coeff_diffuse;"
    "uniform half l_coeff_specular;"
    "uniform half l_specular_exp;"

    "half4 apply_light(half3 EYE, half3 N, half4 c) {"
    "half3 LR = reflect(-l_vec*side_select, N);"
    "half s_base = max(dot(normalize(EYE), LR), 0),"

    "a = l_coeff_ambient,"
    "d = l_coeff_diffuse * max(dot(l_vec, N), 0),"
    "s = l_coeff_specular * saturate(pow(s_base, l_specular_exp));"

    "c.rgb = (a + d*l_color)*c.rgb + s*l_color*c.a;"

    "return c;"
    "}";

static sk_sp<SkRuntimeEffect> sphere_fancylight_effect()
{
    static const SkRuntimeEffect *effect =
        SkRuntimeEffect::MakeForShader(SkStringPrintf(gSphereSkSL, gFancyLightSkSL), {}).effect.release();
    if (0 && !effect) {
        printf("!!! %s\n",
            SkRuntimeEffect::MakeForShader(SkStringPrintf(gSphereSkSL, gFancyLightSkSL), {}).errorText.c_str());
    }
    SkASSERT(effect);

    return sk_ref_sp(effect);
}

static sk_sp<SkRuntimeEffect> sphere_basiclight_effect()
{
    static const SkRuntimeEffect *effect =
        SkRuntimeEffect::MakeForShader(SkStringPrintf(gSphereSkSL, gBasicLightSkSL), {}).effect.release();
    SkASSERT(effect);

    return sk_ref_sp(effect);
}

class SphereNode final : public sksg::CustomRenderNode {
public:
    SphereNode(sk_sp<RenderNode> child, const SkSize &child_size)
        : INHERITED({ std::move(child) }), fChildSize(child_size)
    {}

    enum class RenderSide {
        kFull,
        kOutside,
        kInside,
    };

    SG_ATTRIBUTE(Center, SkPoint, fCenter)
    SG_ATTRIBUTE(Radius, float, fRadius)
    SG_ATTRIBUTE(Rotation, SkM44, fRot)
    SG_ATTRIBUTE(Side, RenderSide, fSide)

    SG_ATTRIBUTE(LightVec, SkV3, fLightVec)
    SG_ATTRIBUTE(LightColor, SkV3, fLightColor)
    SG_ATTRIBUTE(AmbientLight, float, fAmbientLight)
    SG_ATTRIBUTE(DiffuseLight, float, fDiffuseLight)
    SG_ATTRIBUTE(SpecularLight, float, fSpecularLight)
    SG_ATTRIBUTE(SpecularExp, float, fSpecularExp)

private:
    sk_sp<SkShader> contentShader()
    {
        if (!fContentShader || this->hasChildrenInval()) {
            const auto &child = this->children()[0];
            child->revalidate(nullptr, SkMatrix::I());

            SkPictureRecorder recorder;
            child->render(recorder.beginRecording(SkRect::MakeSize(fChildSize)));

            fContentShader = recorder.finishRecordingAsPicture()->makeShader(SkTileMode::kRepeat, SkTileMode::kRepeat,
                SkFilterMode::kLinear, nullptr, nullptr);
        }

        return fContentShader;
    }

    sk_sp<SkShader> buildEffectShader(float selector)
    {
        const auto has_fancy_light = fLightVec.length() > 0 && (fDiffuseLight > 0 || fSpecularLight > 0);

        SkRuntimeShaderBuilder builder(has_fancy_light ? sphere_fancylight_effect() : sphere_basiclight_effect());

        builder.child("child") = this->contentShader();
        builder.uniform("child_scale") = fChildSize;
        builder.uniform("side_select") = selector;
        builder.uniform("rot_matrix") = std::array<float, 9>{
            fRot.rc(0, 0), fRot.rc(0, 1), fRot.rc(0, 2), fRot.rc(1, 0), fRot.rc(1, 1),
            fRot.rc(1, 2), fRot.rc(2, 0), fRot.rc(2, 1), fRot.rc(2, 2),
        };

        builder.uniform("l_coeff_ambient") = fAmbientLight;

        if (has_fancy_light) {
            builder.uniform("l_vec") = fLightVec * -selector;
            builder.uniform("l_color") = fLightColor;
            builder.uniform("l_coeff_diffuse") = fDiffuseLight;
            builder.uniform("l_coeff_specular") = fSpecularLight;
            builder.uniform("l_specular_exp") = fSpecularExp;
        }

        const auto lm = SkMatrix::Translate(fCenter.fX, fCenter.fY) * SkMatrix::Scale(fRadius, fRadius);

        return builder.makeShader(&lm);
    }

    SkRect onRevalidate(sksg::InvalidationController *ic, const SkMatrix &ctm) override
    {
        fSphereShader.reset();
        if (fSide != RenderSide::kOutside) {
            fSphereShader = this->buildEffectShader(1);
        }
        if (fSide != RenderSide::kInside) {
            auto outside = this->buildEffectShader(-1);
            fSphereShader = fSphereShader ?
                SkShaders::Blend(SkBlendMode::kSrcOver, std::move(fSphereShader), std::move(outside)) :
                std::move(outside);
        }
        SkASSERT(fSphereShader);

        return SkRect::MakeLTRB(fCenter.fX - fRadius, fCenter.fY - fRadius, fCenter.fX + fRadius, fCenter.fY + fRadius);
    }

    void onRender(SkCanvas *canvas, const RenderContext *ctx) const override
    {
        if (fRadius <= 0) {
            return;
        }

        SkPaint sphere_paint;
        sphere_paint.setAntiAlias(true);
        sphere_paint.setShader(fSphereShader);

        canvas->drawCircle(fCenter, fRadius, sphere_paint);
    }

    const RenderNode *onNodeAt(const SkPoint &) const override
    {
        return nullptr;
    } // no hit-testing

    const SkSize fChildSize;

    // Cached shaders
    sk_sp<SkShader> fSphereShader;
    sk_sp<SkShader> fContentShader;

    // Effect controls.
    SkM44 fRot;
    SkPoint fCenter = { 0, 0 };
    float fRadius = 0;
    RenderSide fSide = RenderSide::kFull;

    SkV3 fLightVec = { 0, 0, 1 }, fLightColor = { 1, 1, 1 };
    float fAmbientLight = 1, fDiffuseLight = 0, fSpecularLight = 0, fSpecularExp = 0;

    using INHERITED = sksg::CustomRenderNode;
};

class SphereAdapter final : public DiscardableAdapterBase<SphereAdapter, SphereNode> {
public:
    SphereAdapter(const skjson::ArrayValue &jprops, const AnimationBuilder *abuilder, sk_sp<SphereNode> node)
        : INHERITED(std::move(node))
    {
        enum : size_t {
            //      kRotGrp_Index =  0,
            kRotX_Index = 1,
            kRotY_Index = 2,
            kRotZ_Index = 3,
            kRotOrder_Index = 4,
            // ???                =  5,
            kRadius_Index = 6,
            kOffset_Index = 7,
            kRender_Index = 8,

            //       kLight_Index =  9,
            kLightIntensity_Index = 10,
            kLightColor_Index = 11,
            kLightHeight_Index = 12,
            kLightDirection_Index = 13,
            // ???                = 14,
            //     kShading_Index = 15,
            kAmbient_Index = 16,
            kDiffuse_Index = 17,
            kSpecular_Index = 18,
            kRoughness_Index = 19,
        };

        EffectBinder(jprops, *abuilder, this)
            .bind(kOffset_Index, fOffset)
            .bind(kRadius_Index, fRadius)
            .bind(kRotX_Index, fRotX)
            .bind(kRotY_Index, fRotY)
            .bind(kRotZ_Index, fRotZ)
            .bind(kRotOrder_Index, fRotOrder)
            .bind(kRender_Index, fRender)

            .bind(kLightIntensity_Index, fLightIntensity)
            .bind(kLightColor_Index, fLightColor)
            .bind(kLightHeight_Index, fLightHeight)
            .bind(kLightDirection_Index, fLightDirection)
            .bind(kAmbient_Index, fAmbient)
            .bind(kDiffuse_Index, fDiffuse)
            .bind(kSpecular_Index, fSpecular)
            .bind(kRoughness_Index, fRoughness);
    }

private:
    void onSync() override
    {
        const auto side = [](ScalarValue s) {
            switch (SkScalarRoundToInt(s)) {
                case 1:
                    return SphereNode::RenderSide::kFull;
                case 2:
                    return SphereNode::RenderSide::kOutside;
                case 3:
                default:
                    return SphereNode::RenderSide::kInside;
            }
            SkUNREACHABLE;
        };

        const auto rotation = [](ScalarValue order, ScalarValue x, ScalarValue y, ScalarValue z) {
            const SkM44 rx = SkM44::Rotate({ 1, 0, 0 }, SkDegreesToRadians(x)),
                        ry = SkM44::Rotate({ 0, 1, 0 }, SkDegreesToRadians(y)),
                        rz = SkM44::Rotate({ 0, 0, 1 }, SkDegreesToRadians(-z));

            switch (SkScalarRoundToInt(order)) {
                case 1:
                    return rx * ry * rz;
                case 2:
                    return rx * rz * ry;
                case 3:
                    return ry * rx * rz;
                case 4:
                    return ry * rz * rx;
                case 5:
                    return rz * rx * ry;
                case 6:
                default:
                    return rz * ry * rx;
            }
            SkUNREACHABLE;
        };

        const auto light_vec = [](float height, float direction) {
            float z = std::sin(height * SK_ScalarPI / 2), r = std::sqrt(1 - z * z), x = std::cos(direction) * r,
                  y = std::sin(direction) * r;

            return SkV3{ x, y, z };
        };

        const auto &sph = this->node();

        sph->setCenter({ fOffset.x, fOffset.y });
        sph->setRadius(fRadius);
        sph->setSide(side(fRender));
        sph->setRotation(rotation(fRotOrder, fRotX, fRotY, fRotZ));

        sph->setAmbientLight(SkTPin(fAmbient * 0.01f, 0.0f, 2.0f));

        const auto intensity = SkTPin(fLightIntensity * 0.01f, 0.0f, 10.0f);
        sph->setDiffuseLight(SkTPin(fDiffuse * 0.01f, 0.0f, 1.0f) * intensity);
        sph->setSpecularLight(SkTPin(fSpecular * 0.01f, 0.0f, 1.0f) * intensity);

        sph->setLightVec(
            light_vec(SkTPin(fLightHeight * 0.01f, -1.0f, 1.0f), SkDegreesToRadians(fLightDirection - 90)));

        const auto lc = static_cast<SkColor4f>(fLightColor);
        sph->setLightColor({ lc.fR, lc.fG, lc.fB });

        sph->setSpecularExp(1 / SkTPin(fRoughness, 0.001f, 0.5f));
    }

    Vec2Value fOffset = { 0, 0 };
    ScalarValue fRadius = 0, fRotX = 0, fRotY = 0, fRotZ = 0, fRotOrder = 1, fRender = 1;

    ColorValue fLightColor;
    ScalarValue fLightIntensity = 0, fLightHeight = 0, fLightDirection = 0, fAmbient = 100, fDiffuse = 0, fSpecular = 0,
                fRoughness = 0.5f;

    using INHERITED = DiscardableAdapterBase<SphereAdapter, SphereNode>;
};
} // namespace

sk_sp<sksg::RenderNode> EffectBuilder::attachSphereEffect(const skjson::ArrayValue &jprops,
    sk_sp<sksg::RenderNode> layer) const
{
    auto sphere = sk_make_sp<SphereNode>(std::move(layer), fLayerSize);

    return fBuilder->attachDiscardableAdapter<SphereAdapter>(jprops, fBuilder, std::move(sphere));
}
} // namespace skottie::internal
